Changes in cervical stiffness during pregnancy: Preliminary assessment with shear wave elasticity imaging in the rhesus macaque

The stiffness of the uterine cervix changes during pregnancy, significantly softening at term. A pathologically rapid softening can result in preterm birth. Shear Wave Elasticity Imaging (SWEI) methods can be used to track these changes. Difficulties of in vivo human research during pregnancy motivate the study of animal models with anatomy and physiology similar to humans. This work presents preliminary results of the use of SWEI methods to assess cervical stiffness changes during pregnancy in a rhesus macaque non-human primate (NHP) model. Pregnant NHP subjects are being scanned during two consecutive menstrual cycles before pregnancy and five times between weeks 4 to 23 after conception and once two weeks after delivery. Shear waves are remotely induced with an Acoustic Radiation Force Impulse excitation within regions of interest (ROIs) centered in the uterine end of cervix. Shear wave speed (SWS) was quantified with different estimators and at various ROI locations to choose the more consistent and precise estimates. From 25 subjects currently enrolled, 8 have successfully completed the study. At late pregnancy, SWS values significantly decreased to less than 40% of their pre-pregnancy values, and recovered two weeks after delivery. SWS changes in the same subject at early pregnancy compared to pre-pregnancy and late-pregnancy values were statistically significant. Our results motivate further investigation of SWEI to track cervical softening during pregnancy in the NHP model.